The Vatican summons a conclave of cardinals that must begin 15-20 days after Benedict's Feb. 28 resignation.

Cardinals eligible to vote — those under age 80 — are sequestered within Vatican City and take an oath of secrecy.

Any baptized Roman Catholic male is eligible for election as pope, but only cardinals have been selected since 1378.

Two ballots held each morning and two each afternoon in the Sistine Chapel. A two-thirds majority is required. Benedict in 2007 reverted back to this two-thirds majority rule, reversing a 1996 decision by Pope John Paul II, who had decreed that a simple majority could be invoked after about 12 days of inconclusive voting.

Ballots are burned after each round. Black smoke means no decision; white smoke signals that cardinals have chosen pope and he has accepted. Bells also signal the election of a pope to help avoid possible confusion over color of smoke coming from chimney of the Sistine Chapel.

The new pope is introduced from the loggia overlooking St. Peter's Square with the words "Habemus Papam!" (Latin for "We have a pope!") and he imparts his first blessing.